Techniques have been proposed to change an operation mode of a wind turbine power generating apparatus to protect the wind turbine power generating apparatus under harsh weather conditions such as a high wind velocity.
For instance, Patent Document 1 discloses a method of continuously operating a wind turbine power generating apparatus in a high wind-velocity range on or above a critical wind velocity. Patent Document 1 discloses controlling the pitch angle of wind turbine blades to reduce an output non-continuously in accordance with the wind velocity in a high wind-velocity range on or above a critical wind velocity.